The present invention relates to an insulating film of a semiconductor device and a coating solution for forming the insulating film and a method of manufacturing the insulating film, and in particular, relates to an improvement in an insulating film which is provided between metal wiring lines formed on a large scale semiconductor integrated circuit, and a coating solution for forming the insulating film, and a method of manufacturing the insulating film.
In the prior art, with the progress in microminiaturization and high integration of a semiconductor device, a width of a device element and an interval between elements, for example, a width of a metal wiring line and its interval have been decreased more and more. In contrast, a height of the element such as the metal wiring line has not substantially been reduced for the reason that a wiring resistance and a current density cannot be increased to a great extent. Accordingly, in recent semiconductor devices, the interval between the metal wiring lines in a lateral direction is very narrow, and the height of the wiring line is still high. In such a large scale semiconductor integrated circuit, the aspect ratio of a height to a width of the metal wiring line has been increased remarkably. Such a trend of increase of the aspect ratio is not limited to the metal wiring line, and it is similar also in other device elements.
As an interlayer Insulating film which is formed on various elements such as the metal wiring lines of a high aspect ratio, it is required not only to insure insulation between the elements but also to have an excellent filling property which enables to fill up between the elements without leaving a void and to fill completely between the elements.
Furthermore, in order to insure a focus margin in lithography process conducted after formation of the interlayer insulating film, an excellent property for forming a planar surface is required, which enables to sufficiently moderate surface irregularities or undulation in the interlayer insulating film.
As the insulating film which can be filled between narrow elements as mentioned above, for example, there is a silicon oxide thin film formed by a chemical vapor deposition method by thermal decomposition or plasma decomposition of monosilane. However, in the insulating film (silicon oxide thin film) formed by this method, voids are apt to be formed between the elements, and actually, a sufficient filling property and a planarizing property are not obtained.
Accordingly, as the method of forming an insulating film which is excellent in the filling property of a narrow space between elements, there is a method of forming an insulating film by chemical vapor deposition by ozone oxidation of an organic silane as disclosed in Japanese Patent Laid-Open Publication No. 61-77695.
Furthermore, as disclosed in Japanese Patent Laid-Open Publication No. Hei 3-203240, there is an insulating film having a multilayer structure including a spin-on glass film (hereinafter referred to as an xe2x80x9cSOGxe2x80x9d film). In this prior art insulating film, an advantage is provided which enables to achieve a planar surface of the insulating film, because the occurrence of a crack in the SOG film can be prevented even when the SOG film is coated to a large thickness.
Furthermore, there is another prior art technique in which after filling a narrow space between the elements with an insulating film formed by chemical vapor deposition, an insulating film is further grown over the whole surface to a large thickness, and thereafter, an unnecessary insulating film is removed by a chemical mechanical polishing technique (CMP) thereby to achieve a planar surface of the insulating film.
However, in the insulating film formed by the method disclosed in the Japanese Patent Laid-Open Publication No. 61-77695, although the filling property of a narrow space between the elements is excellent, on the other hand, there is a drawback that a film thickness becomes thin when the insulating film is formed on a pad or a flat and wide interval between the elements. Accordingly, there is a problem that planarization cannot be achieved over the whole region of the surface.
Furthermore, in the insulating film having a multilayer structure including an SOG film obtained by the method disclosed in the Japanese Patent Laid-Open Publication No. Hei 3-203240, although the occurrence of a crack in the SOG film is prevented to some extent, there is a problem that peeling and crack are easily occurred in a film other than the SOG film constituting the above-mentioned insulating film due to a difference in a shrinkage ratio between the SOG film and the other film. Furthermore, there is a problem that planarization cannot be achieved sufficiently over the whole region of the surface.
Furthermore, in the prior art in which the chemical vapor deposition technique is combined with the chemical mechanical polishing technique, it is possible to insure the planar surface formation over the whole region of the semiconductor substrate depending on conditions, however, there is a problem that the setting of the conditions is difficult. Moreover, there is a problem that expensive apparatus is needed, and this leads to a large increase in costs. There is another problem that the detection of an end point is difficult in the chemical mechanical polishing, and non-uniformity between the wafers is large and the throughput is low. Furthermore, there is a problem that the yield is low due to the occurrence of contamination and particles.
The present invention solves the problems in the prior art as mentioned above, and it is an object to provide an insulating film of a semiconductor device and an insulation film forming coating solution for forming the insulating film and a method of manufacturing the insulating film, which of course enables to obtain a good film quality wherein the shrinkage ratio is small, and the oxygen plasma resistant property and the etching workability are excellent and the crack is not occurred, and also the excellent filling property and the formation of a thick film and the planar surface forming property are simultaneously achieved.
In order to achieve the object, the invention in claims 1 and 2 relates to an insulating film of a semiconductor device, and it provides an insulating film of a semiconductor device characterized in that the insulating film comprises a silane-derived compound expressed by a general formula, SiHx(CH3)yO2xe2x88x92(x+y)/2 (where, 0 less than x less than 1, 0 less than y less than 1, x+yxe2x89xa61).
Furthermore, the invention of claims 3 to 5 relates to an insulating film forming coating solution for forming an insulating film of a semiconductor device, and it provides an insulating film forming coating solution containing as a main component a solution of a polymer obtained by co-hydrolysis of.
trialkoxysilane expressed by a general formula, SiH (OR)3, and
methyltrialkoxysilane expressed by a general formula, SiCH3(OR)3.
Furthermore, the invention of claims 6 to 8 relates to an insulating film forming coating solution for forming an insulating film of a semiconductor device, and it provides an insulating film forming coating solution containing as a main component a solution of a polymer obtained by co-hydrolysis of,
tetraalkoxysilane expressed by a general formula, Si (OR)4,
trialkoxysilane expressed by a general formula, SiH (OR)3, and
methyltrialkoxysilane expressed by a general formula, SiCH3(OR)3.
Furthermore, the invention of claims 9 relates to a method of forming an insulating film of a semiconductor device, and it provides a method of forming an insulating film comprising the steps of coating the insulating film forming coating solution described in any of claims 3 to 8 on a semiconductor substrate having a desired pattern formed thereon, and drying the coated insulating film forming coating solution and thereafter heating and curing in an inert gas atmosphere.
The insulating film described in claims 1 and 2 is comprised of the silane-derived compound expressed by the general formula, SiHx(CH3)yO2xe2x88x92(x+y)/2 (where, 0 less than x less than 1, 0 less than y less than 1, x+yxe2x89xa61), and thus, the insulating film has a structure having H (hydrogen) which is directly bonded to Si (silicon) and which is introduced into the insulating film. Accordingly, in the insulating film, the shrinkage rate is reduced without impairing the oxygen plasma resistant property and the etching workability.
Furthermore, in view of the oxygen plasma resistant property and the etching workability, it is preferable that yxe2x89xa60.8, and in view of the crack resistant property, it is preferable that 0.2xe2x89xa6y.
The reason for this will be described below. The usual SOG film which has been used in the prior art includes O (oxygen), and C (carbon) of a methyl group which are counterparts for directly bonding to Si. When Si bonds to only O, with respect to Sixe2x80x94OR or Sixe2x80x94OH in the coating film, end groups are bonded to each other during curing process, and a crosslinked network of Sixe2x80x94Oxe2x80x94Si is developed. Thus, the shrinkage rate is increased, and the film becomes fragile since the hardness is increased. As a result, cracks are easily occurred, and a thick film having a thickness of 3000 xc3x85 or larger cannot be formed.
On the other hand, when the methyl group is introduced into Si to the extent having a maximum ratio of Si:C=2:1, the shrinkage rate of the obtained insulating film can be reduced, and at the same time, the film is made flexible, and it is possible to form a film having a maximum thickness of about 5000 xc3x85. However, the shrinkage rate of the film cannot be reduced to lower than about 7%.
Accordingly, in order to reduce the shrinkage rate of the above-mentioned film and to form a thick film, when the content of C (an introduced quantity of methyl group) in the insulating film is increased, then the Sixe2x80x94C bond is oxidized and decomposed, and the oxygen plasma resistant property is degraded. Furthermore, since the reaction with CHF3 contained in etching gas occurs to produce a great amount of fluorocarbon polymer, a problem arises in which the etching workability is degraded to a great extent.
Here, the action to reduce the shrinkage rate of the above-mentioned film and to make the film flexible is caused by the presence of C due to the introduction of the methyl group. In other words, due to the presence of C, the number of O bonded to Si is reduced from 4 to 3, and the remaining bond is Sixe2x80x94C so that the shrinkage rate of the film is reduced and the flexibility of the film is improved. This effect can be also obtained by using the bond of Sixe2x80x94H in place of the Sixe2x80x94C. Accordingly, it is possible to reduce the shrinkage rate of the film and to make the film flexible by increasing the amount of H without increasing the amount of C present in the insulating film. As a result, the shrinkage rate of the insulating film is reduced and the formation of a thick film can be achieved without degrading the oxygen plasma resistant property and the etching workability.
Furthermore, by introducing the Sixe2x80x94H bond, the reduction of the water absorption property and the water resistant property of the insulating film can be attained as a result of a strong hydrophobic nature of the Sixe2x80x94H bond.
Also, the dielectric constant is decreased due to the reduction of water content, and when the film is used as an interlayer insulating film between metal wiring lines, an advantage of reducing a parasitic capasitance is obtained.
Since the insulating film forming coating solution in claims 3 to 5 is a liquid, the coating solution can be filled up into a narrow gap of an underlying step portion with priority, and the filling property is improved and at the same time, the planarization can be achieved.
Furthermore, the insulating film obtained by drying the insulating film forming coating solution has a structure in which H which directly bonds to Si is introduced. Accordingly, in the insulating film, the number of O which bonds to Si is reduced from 4 to 3, and the remaining bond is Sixe2x80x94H or Sixe2x80x94C. As a result, the amount of H is increased without increasing the amount of C which is present in the insulating film, and thus, the shrinkage rate of the film is reduced and the film can be made flexible. For this reason, the shrinkage rate of the insulating film is reduced, and the formation of a thick film can be achieved without degrading the oxygen plasma resistant property and the etching workability.
Here, as the trialkoxysilane expressed by the general formula, SiH (OR)3, for example, trimethoxysilane, triethoxysilane, or the like is suitably used.
Furthermore, as the methyltrialkoxysilane expressed by the general formula, SiCH3 (OR)3, methyltrimethoxysilane, methyltriethoxysilane, or the like is suitably used.
Also in the hydrolysis, besides water, an acid such as formic acid, acetic acid, phosphoric acid, hydrochloric acid, may be used as a catalyst.
Furthermore, in the hydrolysis, another organic silane group such as dimethyldiethoxysilane, phenyltrimethoxysilane, or the like may be mixed as a modifying agent.
Furthermore, both the catalyst and the modifying agent may be jointly mixed.
The molecular weight of a polymer obtained by the hydrolysis can be changed by a temperature, a time, and a concentration in a condensation and polymerization method. However, when the molecular weight exceeds about 100000, the polymer becomes insoluble to a solvent. Thus, it is desirable that the molecular weight of the polymer is equal to 100000 or less.
Furthermore, when the molecular weight is less than 1000, the amount of the polymer which is not cured but volatized by heating is increased. Accordingly, it is desirable that the molecular weight of the polymer is equal to 1000 or larger.
Furthermore, preferably, the molecular weight is suitable when it is about 1500 to 10000.
The polymer which is obtained in the hydrolysis is soluble to various of solvents, and in particular, lower alchohol such as methanol, ethanol, 2-propanol, or the like, glycol-ethers such as 2-ethoxyethanol, or the like, ketons such as methyl-isobutylketon or the like, carbolic-acid esters such as isobutylacetate or the like may be suitably used. However, when the boiling point of the solvent is low, the drying progresses too fast, and peeling or cracking is caused sometimes. On the other hand, when the boiling point is too high, it takes a long time for drying. Accordingly, it is preferable to use a solvent having an intermediate boiling point of about 100 to 180xc2x0 C.
Furthermore, if the concentration of the solution of the above-mentioned polymer is too high, striation and defective filling are apt to be caused, and if the concentration of the solution of the above-mentioned polymer is too low, a film thickness obtained by one time of coating will be thin. Accordingly, the concentration of the solution of the above-mentioned polymer is suitably 5 to 50 weight %.
As the insulating film forming coating solution in claims 6 to 8 is a liquid, the coating solution can be filled up a narrow gap in an underlying step portion with priority, and thus, the filling property is improved and the planarization can be achieved.
Furthermore, the insulating film obtained by coating and drying the insulating film forming coating solution has a structure in which H which is bonded directly to Si is introduced. Accordingly, in the insulating film, the number of O which is bonded to Si is reduced from 4to 3, and the remaining bond is Sixe2x80x94H or Sixe2x80x94C. Thus, the shrinkage rate of the film can be reduced and the film can be made flexible by increasing the amount of H without increasing the amount of C.
As a result, the shrinkage rate of the insulating film is reduced and the formation of a thick film can be achieved without impairing the oxygen plasma resistant property and the etching workability.
In the insulating film forming coating solution, tetraalkoxysilane expressed by the general formula, Si (OR)4, trialkoxysilane expressed by the general formula, SiH (OR)3, and methyltrialkoxysilane expressed by the general formula, SiCH3 (OR)3 are co-hydrolized, alternatively, the tetraalkoxysilane, trialkoxysilane, and methyltrialkoxysilane are individually hydrolized and polymerized, and the resultant products may be mixed.
As the tetraalkoxysilane expressed by the general formula, Si (OR)4 for example, tetramethoxysilane, tetraethoxysilane, or the like is suitably used.
As the trialkoxysilane expressed by the general formula, SiH (OR)3, similar compounds listed in the description of the action relating to claim 2 are suitably used.
As the methyltrialkoxysilane expressed by the general formula, SiCH3 (OR)3, similar compounds listed in the description of the action relating to claims 3 to 5 are suitably used.
Furthermore, also in the hydrolysis mentioned above, the catalyst or the modifying agent listed in the description of the action relating to claim 2 may be mixed, or both the catalyst and the modifying agent may be jointly mixed.
The molecular weight of the polymer obtained by the hydrolysis is desirably equal to 1000 or more, or equal to 100000 or less for the same reason as described as to the action in claims 3 to 5. It is further preferable to select the molecular weight about 1500 to 10000.
As the solvent which is usable with the polymer obtained in the hydrolysis, those solvents listed in the description of the action in claim 2 is used suitably. However, also in this case, when the boiling point of the solvent is low, the drying progresses too fast, and the brushing and cracking might be caused, and when the boiling point of the solvent is too high, it takes a long time for the drying. Thus, it is desirable to use a solvent having an intermediate boiling point of about 100 to 180 xc2x0 C.
Furthermore, when the concentration of the solution of the above-mentioned polymer is too high, striation and defective filling are apt to be caused, and when the concentration of the solution of the above-mentioned polymer is too low, the film thickness obtained by one time of coating will be thin. Accordingly, the concentration of the solution of the above-mentioned polymer is suitable when it is selected to be 5 to 50 weight %.
In the method of manufacturing the insulating film in claim 9, by coating the insulating film forming solution described in any of claims 3 to 8, it is possible to make the insulating film forming solution fill into a narrow recess in the underlying step portion (a desired pattern formed on the semiconductor substrate). Accordingly, the filling property is improved, and the planarization can be achieved.
Furthermore, after drying the coated insulating film, by heating and curing in an inert gas atmosphere, the insulating film forming solution is polymerized and cured without being mixed with oxygen. Accordingly, at the time of polymerization and curing of the insulating film forming solution, the insulating film forming solution is not oxidized. Thus, the insulating film obtained in this process has the structure in which H which is directly bonded to Si is introduced. As a result, in the insulating film, the average number of O which is bonded to Si is equal to 3 or more, and equal to 4 or less, and the remaining bond is Sixe2x80x94H or Sixe2x80x94C. Thus, the shrinkage rate of the film can be reduced and the film can be made flexible. For this reason, the shrinkage rate of the insulating film is reduced and the formation of a thick film is achieved without impairing the oxygen plasma resistant property and the etching workability.
As inert gases, for example, nitrogen, argon,hydrogen, helium, forming gas, or the like may be used suitably.